Characteristic Penetration Depth Research Articles

The evidences for the existence of evanescent wave-induced scattering in the transmission SAXS of high-density polyethylene

In an earlier study of ours (Li et al., IUCrJ,2019 6, 968–983), we conjectured that small-angle X-ray scattering (SAXS) in semicrystalline polymers might be from evanescence wave-induced scattering (Ievi) rather than claimed by classical scattering theory, the incident X-ray-induced scattering (Iin). In this study, we systematically compared Ievi and Iin under the influence of various factors, i.e., linear crystallinity, the number of lamellar crystals (N), the characteristic penetration depth of evanescent wave (dp*) and long period distribution, identifying the method to distinguish SAXS in semicrystalline polymers is from Iin or Ievi. Applying this method to SAXS of a high-density polyethylene (HDPE) sample, it was found that even excluding the influence of instrumental broadening and lamellar thickness/long period dispersity, the SAXS peak in HDPE is still greater than theoretically maximum peak width induced by Iin, indicating the SAXS in HDPE is not induced by incident X-ray directly. Excluding the interference of long period dispersity, it was found that dp* was around 5.9 nm, clearly demonstrating the existence of evanescent wave. Besides, results indicated that the lateral size determined with new theory is accurate, which in turn demonstrated that our assumption that Ievi is from a lamellar stack parallel to incident X-ray is reasonable. Taking all evidences together, it can be concluded safely that SAXS in HDPE is induced by evanescent wave.

Rainy downdrafts in abyssal atmospheres

Context.Results from Juno’s Microwave Radiometer (MWR) indicate nonuniform mixing of ammonia vapor in Jupiter’s atmosphere down to tens of bars, far beneath the cloud level. Helioseismic observations suggest solar convection may require narrow, concentrated downdrafts called entropy rain to accommodate the Sun’s luminosity. Both observations suggest some mechanism of nonlocal convec-tive transport.Aims.We seek to predict the depth that a concentrated density anomaly can reach before efficiently mixing with its environment in bottomless atmospheres.Methods.We modified classic self-similar analytical models of entraining thermals to account for the compressibility of an abyssal atmosphere. We compared these models to the output of high-resolution three-dimensional fluid dynamical simulations to more accurately model the chaotic influence of turbulence.Results.We find that localized density anomalies propagate down to ~3−8 times their initial size without substantially mixing with their environment. Our analytic model accurately predicts the initial flow, but the self-similarity assumption breaks down after the flow becomes unstable at a characteristic penetration depth.Conclusions.In the context of Jupiter, our findings suggest that precipitation concentrated into localized downdrafts of size ~20 km can coherently penetrate to on the order of a hundred kilometers (tens of bars) beneath its initial vaporization level without mixing with its environment. This finding is consistent with expected convective storm length scales and Juno MWR measurements of ammonia depletion. In the context of the Sun, we find that turbulent downdrafts in abyssal atmospheres cannot maintain their coherence through the Sun’s convective layer, a potential challenge for the entropy rain hypothesis.

Model of UV-curing thickness for new thiol-ene resin for additive manufacturing of energetic materials

A new type of photocurable resin, which can be used for additive manufacturing of energetic materials, was prepared by modified polyether and multifunctional mercaptan. For the curing progress of this resin in a single layer of digital light processing (DLP), we incorporate micro-dynamical mechanism of free-radical photopolymerizations into the thickness-time equation to show how the curing thickness varies with initiator concentration ([I]) and incident light intensity ( I 0 ). We show that the temporal variation of curing thickness depends on two key parameters: the characteristic penetration depth h a = 1/(ε 1 [I]+α 0 ), where ε 1 is the molar extinction coefficients of initiator and α 0 is the absorption coefficient of oligomer, and critical time T c = -ln(1-Φ c )/( kI 0 0.5 [I] 0.5 ), where Φ c is the gel point of monomer and k is rate constant. Here, we consider the effects of [I] and I 0 to the characteristic penetration depth h a and the critical time T c in the early stage of radical polymerization, which means that the concentration of initiator and monomer could be deemed as constants. As predicted by the model, T c is a linear function of 1/ I 0 0.5 and 1/[I] 0.5 . Validation experiments show that the curing thickness predicted by the model is in good agreement with the experimental data. These results can be used for the accurate prediction of parameter setting of 3D printing and the component proportion of resin.

Proposal for a Skin Layer-Wise Decomposition Model of Spatially-Resolved Diffuse Reflectance Spectra Based on Maximum Depth Photon Distributions: A Numerical Study

In the context of cutaneous carcinoma diagnosis based on in vivo optical biopsy, Diffuse Reflectance (DR) spectra, acquired using a Spatially Resolved (SR) sensor configuration, can be analyzed to distinguish healthy from pathological tissues. The present contribution aims at studying the depth distribution of SR-DR-detected photons in skin from the perspective of analyzing how these photons contribute to acquired spectra carrying local physiological and morphological information. Simulations based on modified Cuda Monte Carlo Modeling of Light transport were performed on a five-layer human skin optical model with epidermal thickness, phototype and dermal blood content as variable parameters using (i) wavelength-resolved scattering and absorption properties and (ii) the geometrical configuration of a multi-optical fiber probe implemented on an SR-DR spectroscopic device currently used in clinics. Through histograms of the maximum probed depth and their exploitation, we provide numerical evidence linking the characteristic penetration depth of the detected photons to their wavelengths and four source–sensor distances, which made it possible to propose a decomposition of the DR signals related to skin layer contributions.

Effect of sample thickness on concurrent steady spread behavior of floor- and ceiling flames

This paper presents an experimental investigation of the sample thickness effect on the concurrent flame steady spread behavior. Two configurations, ceiling flame and floor flame, as the fundamental diffusion combustion problems and representative scenarios of horizontal flame spread, are concerned herein. PMMA samples with thickness (δ) of 2, 3, 4, 5, 7, 9 mm were employed including both thermally-thin and thermally-thick conditions. A wind tunnel was used to provide the uniform concurrent airflow ranging from 0.3 m/s to 1.2 m/s in 0.3 m/s intervals. Flame characteristics and basic parameters to quantify the flame steady spread process have been studied, including flame spread rate (FSR), equivalent pyrolysis length as well as heat flux feedback in both pyrolysis and preheating zones. Results show that FSR decreases with sample thickness, being more sensitive to sample thickness for ceiling flame configuration than that for floor flame configuration. Equivalent pyrolysis length increases with sample thickness and ceiling flame's equivalent pyrolysis length is larger than floor flame's. Convection feedback is dominant under concurrent airflow regardless of the flame configuration, airflow velocity or sample thickness. In pyrolysis zone, the total heat flux to fuel surface of ceiling flame configuration is larger than that of floor flame configuration for thin samples due to buoyancy, but it decreases rapidly as sample thickness increases. In preheating zone, the heat flux decreases in power law for ceiling flame configuration while a piece-wise fitting is found for floor flame configuration, which is interpreted based on their inherent flame characteristic difference hence the thermal boundary layer conditions between these two configurations. To analyze the sample thickness effect on concurrent flame spread, a characteristic solid temperature (T*) is proposed by theoretical analysis, as an essential parameter to be used in the concurrent flame spread model to represent the coupling effect of heat input in gas phase and in-depth heat loss into the solid phase (or namely thermal inertia controlled by a characteristic thermal penetration depth). The calculated non-dimensional characteristic solid temperature (θ) shows to be less sensitive to flame configuration and concurrent airflow velocity for relatively thicker samples because the thermal penetration depth will tend to approach a limit. A general trend of its variation with sample thickness (δ) can be employed to predict the heat loss into solid phase and its predictive capability is verified by the experimental results. This work advances the fundamental understanding of the sample thickness effect on concurrent flame spread mechanism.

Shear Surface Acoustic Waves in Twinned Piezoelectric Crystals of the $$\bar {6}$$m2 Symmetry Class

Shear surface acoustic waves, whose existence is due to the difference in the signs of piezoelectric modulus tensors of adjoining halves of crystal, are studied on flat interfaces of twinned hexagonal piezoelectric crystals of the $$\bar {6}$$m2 symmetry class. In this case, the inversion axis $$\bar {6}$$ is perpendicular to the interface between the halves. It is shown that, at a weak piezoelectric effect, the characteristic penetration depth of these waves is inversely proportional to the square of component e222 and may significantly exceed the length of the surface wave.

Homogeneity and penetration depth of atmospheric pressure plasma polymerization onto electrospun nanofibrous mats

This work investigates for the first time the penetration depth, nanoscopic homogeneity and conformality of the plasma polymerization onto an electrospun nanofibrous mat. The study is carried out on the model example of atmospheric pressure plasma co-polymerization of anhydride-rich films onto polycaprolactone mats that can find a significant practical applications, for example in tissue engineering and regenerative medicine. Since the surface-to-volume ratio of nanofibrous mats is enormous and the structure of mats resembles extracellular matrix the successful plasma coating of each whole fiber and understanding the penetration of the polymerization into the mat structure are extremely important. The films with reactive anhydride groups were prepared by co-polymerization of maleic anhydride and acetylene using dielectric barrier discharge. The studies were accompanied by the quantification of anhydride groups directly on the PCL electrospun mat using the chemical derivatization with trifluoroethylamine and X-ray photoelectron spectroscopy. The nanoscopic homogeneity and conformality of the anhydride plasma polymer coating on the front side and backside of the nanofibrous mat, 30–40 μm in thickness, did not differ according to the dynamic SIMS mapping. The films containing approximately 6 anhydride groups per 100 carbon atoms coated homogeneously the nanofibers deeper in the PCL mat. The characteristic penetration depth of the deposition was estimated as 46 ± 5 μm.

Acoustic emission characterization of sliding wear under condition of direct and inverse transformations in low-temperature degradation aged Y-TZP and Y-TZP-AL2O3

In this research, results of the investigation of the sliding friction and wear of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) and Y-TZP-Al2O3 samples preliminarily subjected to low-temperature degradation are reported. The investigation was carried out using a pin-on-disk tribometer with simultaneous recording of acoustic emission (AE) and vibration acceleration. The sliding wear process was found to be determined by dynamic direct and inverse Y-TZP transformations detected by monoclinic and tetragonal X-ray diffraction peak ratios. The AE signals generated under direct and inverse transformations can be used to characterize wear and friction mechanisms as well as direct and inversed sliding-induced phase transformations. The AE signal energy grows with the friction coefficient and the inverse transformation degree. Reduction of the AE signal energy indicates establishing the mild wear stage caused by effective stress-induced direct martensitic transformation. The AE signal median frequency increases in the case of lower friction. Numerical studies of wear subsurface fracture under conditions of stress-induced martensitic transformation were used to elucidate the role played by the phase transformation in Y-TZP and Y-TZP-Al2O3. Martensitic transformation in Y-TZP was described with use of the non-associated dilatant plasticity model. Simulation results particularly show that increase in the value of dilatancy coefficient from 0 to 0.2 is accompanied by 25%−30% reduce in characteristic length and penetration depth of sliding-induced subsurface cracks. As shown the AE may be an effective tool for in-situ monitoring the subsurface wear of materials experiencing both direct and inverse transformations.

Direct characterization of the evanescent field in objective-type total internal reflection fluorescence microscopy.

Total internal reflection fluorescence (TIRF) microscopy is a commonly used method for studying fluorescently labeled molecules in close proximity to a surface. Usually, the TIRF axial excitation profile is assumed to be single-exponential with a characteristic penetration depth, governed by the incident angle of the excitation laser beam towards the optical axis. However, in practice, the excitation profile does not only comprise the theoretically predicted single-exponential evanescent field, but also an additional non-evanescent contribution, supposedly caused by scattering within the optical path or optical aberrations. We developed a calibration slide to directly characterize the TIRF excitation field. Our slide features ten height steps ranging from 25 to 550 nanometers, fabricated from a polymer with a refractive index matching that of water. Fluorophores in aqueous solution above the polymer step layers sample the excitation profile at different heights. The obtained excitation profiles confirm the theoretically predicted exponential decay over increasing step heights as well as the presence of a non-evanescent contribution.

New type of surface electromagnetic wave caused by the optical activity of boundary materials

This paper theoretically predicts surface electromagnetic waves on the planar interfaces of media distinguished by gyration pseudotensors that describe natural optical activity. A twinned optically active crystal of one of the planal classes 3m, 4mm, or 6mm is discussed whose halves have rotational symmetry axes that coincide in the interface but differ in the signs of the gyration pseudotensors. It is shown that a weakly localized surface wave can propagate perpendicular to the crystal’s symmetry axis. Its dispersion equation is derived, and it is established how the characteristic penetration depth depends on the optical-activity parameter.

Ring-Shaped Microlanes and Chemical Barriers as a Platform for Probing Single-Cell Migration.

Quantification and discrimination of pharmaceutical and disease-related effects on cell migration requires detailed characterization of single-cell motility. In this context, micropatterned substrates that constrain cells within defined geometries facilitate quantitative readout of locomotion. Here, we study quasi-one-dimensional cell migration in ring-shaped microlanes. We observe bimodal behavior in form of alternating states of directional migration (run state) and reorientation (rest state). Both states show exponential lifetime distributions with characteristic persistence times, which, together with the cell velocity in the run state, provide a set of parameters that succinctly describe cell motion. By introducing PEGylated barriers of different widths into the lane, we extend this description by quantifying the effects of abrupt changes in substrate chemistry on migrating cells. The transit probability decreases exponentially as a function of barrier width, thus specifying a characteristic penetration depth of the leading lamellipodia. Applying this fingerprint-like characterization of cell motion, we compare different cell lines, and demonstrate that the cancer drug candidate salinomycin affects transit probability and resting time, but not run time or run velocity. Hence, the presented assay allows to assess multiple migration-related parameters, permits detailed characterization of cell motility, and has potential applications in cell biology and advanced drug screening.

Current-voltage characteristics of tunnel Josephson junctions with a ferromagnetic interlayer

We present a quantitative study of the current-voltage characteristics (CVC) of diffusive superconductor/insulator/ferromagnet/superconductor (SIFS) tunnel Josephson junctions. In order to obtain the CVC we calculate the density of states (DOS) in the F/S bilayer for arbitrary length of the ferromagnetic layer, using quasiclassical theory. For a ferromagnetic layer thickness larger than the characteristic penetration depth of the superconducting condensate into the F layer, we find an analytical expression which agrees with the DOS obtained from a self-consistent numerical method. We discuss general properties of the DOS and its dependence on the parameters of the ferromagnetic layer. In particular we focus our analysis on the DOS oscillations at the Fermi energy. Using the numerically obtained DOS we calculate the corresponding CVC and discuss their properties. Finally, we use CVC to calculate the macroscopic quantum tunneling (MQT) escape rate for the current biased SIFS junctions by taking into account the dissipative correction due to the quasiparticle tunneling. We show that the influence of the quasiparticle dissipation on the macroscopic quantum dynamics of SIFS junctions is small, which is an advantage of SIFS junctions for superconducting qubits applications.

Analysis of the Elastic-plastic Properties of Metallic Materials by Instrumented Spherical Indentation Testing

Spherical indentation testing is regarded as an effective technique for deducing the constitutive properties of metallic materials, e.g. the determination of the stress-strain curve (<r-e curve) from the characteristic loadL vs. penetration depth h curve (L-h curve). However, the uniqueness between the L-h curve and the <r-e curve has not systematically addressed yet. The existence of materials having different constitutive laws but visually indistinguishable L-h curves has been probed, thus requiring the development of refined methodologies for distinguishing such materials in the reverse analysis. These topics are deeply discussed in the present paper. The indentation responses of an aluminum alloy (Al 6082-T6) and of a distinct material having apparently indistinguishable L-h curves are examined via a proper experimental characterization and Finite Element Analysis (FEA). For both materials the strain processes occurring in the subsurface region are especially examined and compared. The analysis probes that the actual constitutive properties of the indented material can be distinguished once proper functions accounting for the strain processes promoted by the indenter are formulated. Based on these findings, a suitable L-h curve expression and a new reverse analysis algorithm ensuring the one-to-one correspondence between the L-h curve and the <r-e curve of the indented materials are proposed.

Humidity variations across the edge of trade wind cumuli: Observations and dynamical implications

Aircraft data are used to analyze the composite horizontal structure of shallow tropical maritime cumulus clouds across the cloud edge into the ambient clear air. The emphasis is on humidity variations, and their implications for cumulus dynamics. The Lyman-α humidity probe has the required fast response and is unaffected by wetting in-cloud. On average the water vapor mixing ratio increases gradually from the clear air towards the cloud edge, and air is often sub-saturated in the outer fringe of the cloud, implying that droplets are evaporating. Similarly, conserved variables such as the total water concentration and the wet equivalent potential temperature gradually transition in the “margin” of cumulus clouds. The gradual change of water vapor mixing ratio and conserved variables across the cloud edge highlights the significance of lateral entrainment and detrainment, and it reveals a characteristic penetration depth of mixing eddies of 10 to 15% of the cloud diameter, or about 50 m. An ∼ 100 m wide region just outside the cloud is generally characterized by negatively buoyant, sinking air. The excess water vapor in this region, also documented in several recent studies, confirms that the negative buoyancy is caused by evaporative cooling in the cloud margin. Although rather weak, this cooling appears strong enough to evoke a dynamical response, even in the relative small trade wind cumuli.

Penetration depth method—novel real‐time strategy for evaluating femoroacetabular impingement

We introduce a new method for computerized real-time evaluation of femoroacetabular impingement (FAI). In contrast to previously presented stress analyses, this method is based on two types of predictions of penetration depths for two rotating bodies: curvilinear and radial penetration depth. This intuitive method allows the analysis of both bony and soft tissue structures (such as cartilage and acetabular labrum) in real time. Characteristic penetration depth patterns were found for different subtypes of FAI, such as cam and pincer pathologies. In addition, correlation between the penetration depths (estimated by applying this method) and the existing contact stresses (estimated by applying the finite element method) of various hip morphologies were found. A strong correlation with predicted stress values existed, with a mean correlation coefficient of 0.91 for the curvilinear and 0.80 for the radial penetration method. The results show that the penetration depth method is a promising, fast, and accurate method for quantification and diagnosis of FAI.

Single Vesicle Millisecond Fusion Kinetics Reveals Number of SNARE Complexes Optimal for Fast SNARE-mediated Membrane Fusion

SNAREs mediate membrane fusion in intracellular vesicle traffic and neuronal exocytosis. Reconstitution of membrane fusion in vitro proved that SNAREs constitute the minimal fusion machinery. However, the slow fusion rates observed in these systems are incompatible with those required in neurotransmission. Here we present a single vesicle fusion assay that records individual SNARE-mediated fusion events with millisecond time resolution. Docking and fusion of reconstituted synaptobrevin vesicles to target SNARE complex-containing planar membranes are distinguished by total internal reflection fluorescence microscopy as separate events. Docking and fusion are SNAP-25-dependent, require no Ca(2+), and are efficient at room temperature. Analysis of the stochastic data with sequential and parallel multi-particle activation models reveals six to nine fast-activating steps. Of all the tested models, the kinetic model consisting of eight parallel reaction rates statistically fits the data best. This might be interpreted by fusion sites consisting of eight SNARE complexes that each activate in a single rate-limiting step in 8 ms.

Surface Polaritons at the Planar Interface of Twinned Dielectric Gyrotropic Media

The closed-form dispersion equation for surface polaritons localized near the planar interface of the semi-infinite halves of the same transparent uniaxial dielectric gyrotropic medium was derived for the case when the gyration vectors of the contacting materials are perpendicular to the interface and oppositely directed to each other. Surface electromagnetic waves can be excited only if the medium is both anisotropic and gyrotropic. Numerical analysis of the phase velocity, decay coefficients, and polarization of the surface polaritons as functions of the gyration parameter was undertaken. It turned out that, for a weakly gyrotropic medium, the characteristic penetration depth of the surface polaritons is inversely proportional to the squared gyration parameter.

Near field properties in the vicinity of gold nanoparticles placed on various substrates for precise nanostructuring

We present theoretical results on the near field distribution in the vicinity of gold particles excited by laser radiation and placed on various substrate materials. The study is directed towards the precise nanostructuring of different material surfaces. The calculations are performed on the basis of the FDTD simulation technique. Metal (Au), semiconductor (Si) and dielectric (SiO2) substrate materials are investigated. Experimental results are shown to confirm the validity of the obtained FDTD simulation results. The results show that the field in the vicinity of the point of contact is enhanced, and the enhancement factor depends on the substrate material, particle size and the wavelength of the incident optical radiation. The characteristic size of the field enhanced area is found to be several times smaller than the gold particle size: for the case of the smallest particle diameter of 40 nm it is about 10 nm. The enhancement factor of the electric field on the substrate surface is highest when the substrate is gold metal and it decreases about two orders of magnitude when dielectric SiO2 substrate is used. The characteristic penetration depth of the enhanced field is within several tens of nanometres and the depth weakly depends on the substrate material and the laser excitation wavelength. The dependence of the gold particle size on the field enhancement factor is investigated as well. The present results can be used to predict and design precise nanostructuring on different materials with gold nanoparticles excited by a femtosecond laser pulse.

Analysis of Evanescent Waves Scattering by a Single Particle in Total Internal Reflection Microscopy

Since its invention in the mid of eighties (1) Total Internal Reflection Microscopy (TIRM) has proven to be an effective technique to measure weak interactions between spherical colloidal particles and surfaces with a resolution of a few femtonewton. It is a single particle evanescent light scattering technique. In an experimental setup a laser beam is coupled into a prism and hits the glass-water interface with an angle slightly above the critical angle of total internal reflection. This generates an evanescent field near the interface that decays in the lower refractive index medium (water) with a characteristic penetration depth which depends on the angle of incidence. A colloidal particle that is dispersed in the medium will scatter light from the evanescent wave if it is in the vicinity of the surface. By registering a scattered intensity it is possible to deduce the particle- substrate distance. Compared to other methods for measure particle wall interactions like the surface force apparatus or the atomic force microscopy where a colloidal particle is attached to the tip, TIRM is the most sensitive technique because thermal fluctuations where limit the other methods in their resolution are exploited to determine the interaction potential. In this way forces in the order of a few femtonewton can be detected. TIRM has proven to be a valuable tool for the precise measurement of weak colloidal interactions as double layer forces, van der Waals forces, magnetic interactions and depletion forces. Review on TIRM can be found for example in (2,3). To compare experimental results with results of mathematical modeling an effective light scattering method is needed. For this purpose the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for light scattering analysis, which has recently been applied for evanescent wave scattering (4). 1. Discrete Sources Method For the theoretical modeling the Discrete Sources Method (DSM) has been chosen. The DSM is a well-known method for the analysis of light scattering. It has recently been applied to the evanescent wave scattering (4). In frame of the DSM the mathematical statement can be presented as follows:

Chemical-specific representation of air--soil exchange and soil penetration in regional multimedia models.

In multimedia mass-balance models, the soil compartment is an important sink as well as a conduit for transfers to vegetation and shallow groundwater. Here a novel approach for constructing soil transport algorithms for multimedia fate models is developed and evaluated. The resulting algorithms account for diffusion in gas and liquid components; advection in gas, liquid, or solid phases; and multiple transformation processes. They also provide an explicit quantification of the characteristic soil penetration depth. We construct a compartment model using three and four soil layers to replicate with high reliability the flux and mass distribution obtained from the exact analytical solution describing the transient dispersion, advection, and transformation of chemicals in soil layers with different properties but a fixed boundary condition at the air-soil surface. The soil compartment algorithms can be dynamically linked to other compartments (air, vegetation, groundwater, surface water) in multimedia fate models. We demonstrate and evaluate the performance of the algorithms in a model with applications to benzene, benzo[a]pyrene, MTBE, TCDD, and tritium.